ies concerning heat sealing process. The effect of heat sealing process variables on seal properties of
polyethylene films was quantitatively determined. They also estimated the required platen tempera-ture
for the highest possible heat seal strength of a semicrystalline polymer with the given dwell time
and interfacial temperature by finite element model. Further more, they reported that the heat seal strength
is primarily controlled by sealing tem-perature and dwell time, rather than pressure. Heat seal strength
versus platen temperature plot has been established in their study. Tetsuya et al. [6] had investigated the
effect of heat sealing tempera-ture on the mechanical properties and morphology of oriented polypropylene
OPPcast polypropy-lene CPP laminate films. They reported that ten-sile strength of the seal was
affected by the orienta-tion of the films. Whilst, Hashimoto et al. [7] had carried out investigation on
the failure criteria of the heat sealed part of OPPCPP heat seals made by impulse type heat sealing
machine. They reported that heat seals were stronger in the transverse direc-tion as compared to the
machine direction.
In the present study, the effect of bar sealing parameters on heat seal strength of OPPMCPP
laminate film was investigated. The effects of vari- ous combination of platen temperature and dwell
time to the process window of the laminate films are also studied in view of to provide a guideline to the
bar sealing users when setting up their machine.
2. Experimental
2.1. Laminate films
The plastic film used in the present study was a commercial OPPMCPP laminate film. The films
were laminated through dry-bond process using a urethane adhesive. The thickness of OPP and
MCPP films were 23 and 25 micrometers, respec-
tively. The final melting temperature,
T
mf
of the sealant layer i. e. MCPP film was 139.4°C as
determined by differential scanning calorimeter at 10°Cmin scan rate starting at 25 to 300°C under a
helium purge gas.
2.2. Making of heat-seals
In the present study, the laminate film was sealed together in the sealant interface i. e. MCPP film to
simulate fin seal formed in practice. The laminate films were first cut into 15 mm wide strips by
Lorentzen Wettre cutter, made in Sweden. This cutter ensured that clean-cut edges are produced to
prevent premature failures in T-peel test.
Heat seals were made in the laboratory using a model HSGETK heat sealer, made in Germany.
This device clamps two pieces of filmstrips between flat, 10 mm wide heated metal bars. The
temperature, pressure and dwell time of the sealing bars are adjustable. Microprocessor programmed
controllers maintained and digitally indicated set temperature for each bar. Both bars were operated
at the same temperature, and kept close between sealing to minimize heat loss and temperature fluc-
tuations. After the heat seal was made, the sand- wich structure was allowed to cool at ambient
conditions.
2.3. Testing of heat-seals
The heat seals were allowed to age at room temper- ature for at least 48 hours to achieve chemical sta-
bilization. Aging of heat-seal was necessary as the strength of seal may change in time, which may due
to the memory of polymer, or thermophysical prop- erties of polymer as the heat seal samples undergo
melting and cooling processes. The sample was then peeled apart at room temperature in tensile tester of
model MICRO 350, using a 100 N load cell. Each leg of the test specimen was clamped in the tensile tester.
The heat seal area of each speci-men was placed at approximately equidistant between the clamps. The
specimen was aligned in the clamps so that the seal line is perpendicular to the direction of pull. The
constant rate of loading 300 mmmin with initial jaws separation of 25 mm was chosen as recommended by
ASTM F88
–85 [8]. The maximum force required to tears apart the seal, and failure mode of each pull was
recorded.
3. Results and discussion
